In semiconductor wafer processing, various surface treatment steps are commonly performed. For example, such surface treatment may include application of a coating on the wafer surface or planarizing an exposed wafer surface prior to subsequent processing steps.
Planarization, such as chemical-mechanical planarization (CMP), is typically performed to achieve a planar surface over a wafer, sometimes referred to as "global planarity." Typically, the planarization process involves a rotating wafer holder that holds a wafer. A slurry is applied to a rotating table or platen which has a polishing pad thereon. The polishing pad is applied to the wafer at a certain pressure to perform the planarization. In some planarization processes, the wafer holder may not rotate, the table or platen may not rotate and/or the platen may be moved in a linear motion as opposed to rotating. There are numerous types of planarization units available which perform the process in different manners.
In many circumstances, even after planarization has been performed, surface nonuniformities of the wafer are present. For example, because of different rotational speeds of the process at the center of the wafer as opposed to the edge of the wafer and different rotational speeds of the rotating table at the center and at the rotating table's periphery, the rate of removal tends to be different across the wafer surface. For example, the removal rate at the edge of the wafer may be higher than at the center of the wafer. Further, for example, the slurry may not be adequately transported to the entire contact area between the wafer and the pad such that further rate of removal differences are created. Slurry transport to the center of the wafer may also be inadequate when the surface is, or becomes as a result of planarization, substantially planar and further planarization is to be performed. This is because no gaps or nonuniformities are available to assist the transport of the slurry to the middle of the contact area. It is desirable to produce a wafer which is substantially uniformly flat across the wafer surface. Nonuniformity of the wafer surface, even after planarization, may be problematic. For example, such nonuniformity may lead to patterning or photolithography problems. Further, such nonuniformity may result in etching at undesirable depths on the wafer surface.
A wafer handling problem may also occur during wafer processing. For example, in some situations, the wafer can slip out of the holder and stick to the pad on the planarization platen. The wafer is then difficult to remove therefrom.
Other surface treatments, such as coating of wafer surfaces also benefit from surface uniformity. For example, uniform coating of photoresist or other polymer coatings on a wafer may be beneficial to a patterning process performed after such coating is applied. Conventionally, vapor priming is one method that has been used, for example, to minimize the amount of photoresist needed during a patterning process. The vapor prime helps "pre-wet" the semiconductor wafer and allows photoresist to flow out more smoothly, and thus more homogeneously. However, elimination of the need for vapor priming would decrease the number of steps in the patterning process.
For the above reasons, surface treatment methods and systems for performing such surface treatments, e.g, planarization, are needed to provide adequate uniformity of surfaces in wafer processing. The present invention as described below provides such improvements and overcomes the problems described above and those problems which will become apparent to one skilled in the art from the detailed description provided below.